What are my options for propagation fog?

Columns - Technology

Fog is an alternative to mist for germination and propagation. Its advantages include more uniform wetting across the plant area, deeper penetration into the foliage, higher efficiency and lower maintenance costs. For propagation, a high relative humidity can be maintained without saturating the growing medium. Fog is also frequently used for evaporative cooling.

Fog vs. mistFog particles are generally considered to be less than 50 microns (0.002 inches) in diameter. The particle size typically used in high pressure greenhouse fog systems is about 10 microns.

Mist consists of particles from 50 to 100 microns. As a comparison, human hair is about 0.004 inches in diameter or about 100 microns. Breaking 1 gallon of water into 50 micron droplets produces about 68 billion droplets of fog.

Injected into the air these tiny water droplets remain suspended until they are evaporated. The smallest particles vaporize almost instantaneously. The larger particles are carried by air currents, gradually becoming smaller until they are vaporized.

Mist particles are much heavier and take much longer to evaporate. These particles are more likely to fall out of the air and wet plant surfaces or saturate the growing medium. If the particles don’t evaporate before nighttime, the potential for disease increases.

Fog for propagationThe humidity in the air affects the evapo-transpiration rate from the leaf surfaces. To achieve good propagation, a balance between humidity and transpiration is needed to allow water and nutrient uptake without excess dehydration.

In a crop with a dense foliage canopy and without much air movement, a boundary layer of moisture approaching saturation develops around the plants. If the growing medium is also saturated, there is a potential for problems from fungi, moss, Botrytis and fungus gnats.

When the air temperature is high and leaf temperature increases, water loss can exceed the ability of plants to take up moisture and stress can build up within the plants. The use of fog at this time can reduce the air temperature and increase the humidity within the plant canopy without saturating the growing medium. With more oxygen in the root zone, faster rooting occurs. Once the root system is established, the relative humidity can be reduced.

Experience is usually the best approach to determining the proper humidity level. The following can be used as a guideline for propagation:

Establishment phase: 60–80 percent relative humidity

Rapid growth phase: 55–70 percent

Hardening phase: 45–50 percent

Another advantage to the fog system is that foliar feeding, insecticides and fungicides can be applied through the system. This saves time and gives a uniform application.

Small budget solutionAn ultrasonic fog generator uses the vibration of a piezoelectric crystal to nebulize the water. The crystal vibrates about 2 million times per second to break the water droplets into 1 to 10 micron size. Fog units are frequently in the produce section of grocery stores and in nightclubs.

Ultrasonic foggers are available in sizes from ½ to 5 gallons per hour. One gallon of water per hour generates enough fog to cover about 500 square feet of growing area to a height of 4 feet. Some units can be connected to perforated PVC pipe to get uniform distribution over the bench area. Cost of these units is between $250 and $1,200.

Fog can also be produced by a system using a high-speed fan with water channeled to the tip of the blades (e.g., Humidifan from Jaybird Manufacturing Inc., www.jaybirdmfg.com). The shearing action as the water exits the blades produces a fine misting fog. The fan distributes the fog above the crop canopy. This system has the advantage of less clogging as no nozzles are used. Larger units tend to be noisy and some growers have had to remove the system because of the high noise level. Cost varies depending on size ($1,000 to $3,000).

Large budget solutionSeveral methods are used to produce large amounts of fog. A typical system uses a high pressure pump, distribution piping and nozzles that break the water stream into very fine droplets. Piston pumps are needed to develop the 800 to 1,200 pounds per square inch pressure to get the 10-20 micron size droplets. Some manufacturers use compressed air to get the atomization.

Most systems available from irrigation equipment suppliers and labeled as fog systems operate on 50 to 60 psi irrigation water and create a droplet size larger than 50 microns. They are really mist systems.

Copper, stainless steel and re-enforced flexible hose are used for piping. Diameter is frequently ¼- or 3⁄8-inch as water supply required is only 1-2 gallons per hour per nozzle. For propagation, lines of pipe are evenly spaced above the crop.

Nozzles are available in plastic, ceramic and stainless steel. Nozzles should have anti-drip check valves to prevent dripping after the system shuts off. An integral strainer can keep the nozzles from clogging.

The greatest problem associated with fogging systems is nozzle clogging from chemical and particulate matter. Calcium deposits can coat the inside of the pipe and nozzles reducing flow. De-ionized water or rain water can solve the calcium deposit problem.

Several levels of filtration of particulate matter should be installed. The final filter should have a one or two mesh.

Controlling fog systemsFog systems can be controlled with time clocks, a mechanical sensor or humidistat. The time clocks operate so that the fog is turned on for several seconds, several times a minute.

Fog systems can also be operated with a controller or computer that measures vapor pressure deficit (VPD). The difference between saturation water vapor pressure and ambient water vapor pressure is the VPD and represents the evapo-transpirational demand of the surrounding atmosphere as well as the proximity to the dew point. Due to the fact that relative humidity varies with temperature, it is better to manage propagation with VPD. By maintaining the VPD below one, water stress within the plants can be kept at an acceptable level.

Remember Jack

Departments - Outlook

There is going to be something missing for me this year at the California Spring Trials.

There is going to be something missing for me this year at the California Spring Trials. That “something” is the anticipation I usually feel as I pull into the parking lot of the Ecke Ranch first thing Saturday morning. I could always count on technical advisor Jack Williams to be standing at the entrance waiting to take me through the trials. As many of you know, Jack died Oct. 18, 2010, at the age of 54.

Jack brought a sense of excitement to my trial visit -- that I was about to experience something unique. Jack was my host for the coming-out event for Ecke’s new varieties. His enthusiasm was contagious and made me want to find out more about the plants, production specifics, uses and retail/consumer benefits.

Jack, who was a 26-year Ecke employee, served on the OFA board of directors and was a member of the association’s grower committee for 15 years. During his time on the committee, he served 10 years as chair or co-chair.

The Ecke Ranch is planning to include a Jack Williams Memorial tribute display at the trials. Ecke marketing creative consultant Snow Maestas said the display is meant to give visitors an opportunity to remember Jack and spend some quiet moments in reflection.

Educating the industryJack was always a strong proponent of education, so it is fitting that OFA is establishing a scholarship fund in his memory. OFA will manage the fund as part of its Scholars Program (www.ofa.org/scholars.aspx).

Through his involvement with OFA, Jack was instrumental in developing new educational concepts, working to keep programs fresh and introducing new speakers and topics to the OFA Short Course. He developed a grower interactive, on-the-fly, hot-topic session that benefitted growers and trade show exhibitors. He was always an entertaining and informative speaker and facilitator at the Short Course and OFA outreach educational workshops. Jack also wrote articles for the OFA Bulletin and OFA Tips book series, as well as for numerous trade publications, including Greenhouse Management.

Culture: Eriogonum

Departments - Culture

Eriogonum allenii ‘Little Rascal’ (shale barrens buckwheat) from Jelitto Perennial Seeds originated in Virginia and West Virginia. This drought-tolerant, durable plant flowers from June through September. It has an upright habit reaching 16 inches tall with golden yellow flowers and 16 inches wide. Its grey-green paddle-shaped leaves form tight rosettes.

‘Little Rascal’ grows best in full sun, and can be used in rock gardens, dry area landscapes and mixed containers. It prefers well-drained soils with a pH of 5.5-6.5

Seed should be sown into open flats or 72-cell plug trays filled with a well-drained growing medium with a slightly alkaline to neutral pH. The seed should be sown with two to three seeds per cell. Seed is best sown from March through November.

Sow seed and provide even moisture and a temperature of 68°F-72°F. If germination does not occur after three to four weeks, a cooling period of two to four weeks is recommended.

Plugs should be ready to transplant in four to six weeks. Transplant one to two plugs per 4½-inch pot and two to three plugs for 6-inch and larger. Plants should be ready for sale in six to eight weeks.

Plants should be grown at day time temperatures of 60°F-65°F and night temperatures of 50°F-55°F. During the short days of winter, provide night interruption lighting (chrysanthemum lighting) of four hours between 10 p.m. and 2 a.m.

Fertilize plants once a month with 100-150 parts per million nitrogen. No plant growth regulators are needed. Plants do not have any major pest or disease problems.

Variety Notebook

Departments - Variety Notebook

Penstemon ‘Prairie Twilight’Penstemon ‘Prairie Twilight’ from Blooms of Bressingham produces a myriad of small tubular flowers with white tips and throats. Plants have wide, lance-shaped leaves and sturdy stems. It has a long bloom time from late May through July.

Vigorous plants reach 22 inches tall and spread to 26 inches. It can also be used as an upright element in sunny perennial borders and in containers. ‘Prairie Twilight’ was selected by University of Nebraska horticulture professor Dale Lindgren. It is hardy to USDA Hardiness Zones 4 to 9.

Glory stockVarieties in the Matthiola incana Glory series from American Takii do not require as much of a cold period for bud initiation as other varieties. Colors include White Improved, Rose, Cherry, Lavender, Pink and Blue. These columnar type stock plants reach a height of 30-36 inches. They are very early to flower finishing in three to four weeks from a 200-cell plug.

The growing medium pH should be kept between 5.5 to 6.5 and the electrical conductivity level under 0.3. If the temperature is too cold during the seedling stage the plants will be short.

Selection of doubles can be done about two weeks after sowing. Doubles are usually taller, have larger cotyledons and have cotyledons that are lighter green in color. White Improved is earliest blooming by seven to 10 days.

‘Savannah Sunset’ leonotis
Leonotis menthifolia ‘Savannah Sunset’ from Skagit Gardens Inc. is a perennial grown for its showy and unusual whorls of two-lipped, furry, orange tubular flowers. It has square stems and aromatic foliage. Plants bloom from July through October. It can be used as a cut flower, in landscape beds and as a specimen plant.

Say What? Letters, e-mails, posts and comments

Departments - Say What?

Last November’s election significantly changed the landscape in Washington, D.C. Republicans gained control of the House. Democrats retained control of the Senate, but just barely. We have yet to see what impact that may have on the political climate on Capitol Hill.

In a Republican-controlled House, expect to see more small business-friendly legislation aimed at increasing loan opportunities and investment in start-ups. The GOP will emphasize the toll that tax rates take on small business. Economic security and job creation should take center stage, highlighting small businesses as employers and as engines of economic growth.

Immigration reform
Many of the new legislators campaigned on a conservative immigration platform. With an enforcement-first mentality, many lawmakers will push for more aggressive tactics against illegal immigrants. As a result, both comprehensive reform and AgJOBS, which the floral industry has supported for many years, appear to be dead for the foreseeable future.

Estate tax relief
President Obama signed into law the tax bill that sets the estate tax at a rate of 35 percent and an exemption level of $5 million. While this was a positive step forward, the rate and exemption levels remain in place for only two years. The industry needs to continue to work hard at making the estate tax relief permanent.

2012 Farm Bill
For the first time the 2008 Farm Bill included specific specialty crop-related provisions thanks to the work of the Specialty Crop Farm Bill Alliance, including SAF. One of the most important developments was new funding to USDA-APHIS for improved pest and disease prevention and management.

The next Farm Bill is due in 2012. Although Democratic chairmen of the agriculture subcommittees were major supporters of specialty crops in the past, their power is now reduced. Farm Bill monies can be targeted for cuts because they are discretionary and not mandatory, so the outlook for specialty crop funding is not good.

Quarantines and invasivenessAs global trade increases, the pressure on the ornamentals industry has intensified to stop or control the movement of invasives that travel with plants and flowers.
SAF continues to devote considerable resources to representing the industry’s interests, focusing on attempts to prevent quarantine restrictions, specifically problems at ports of entry, international trade restrictions and the steadily increasing call for nursery certification.

Drew Gruenburg is chief operating officer, Lin Schmale is senior director of government relations, Jeanne Ramsay is senior director of government relations, Society of American Florists, (800) 336-4743; www.safnow.org.

For more: about these issues and others that will impact the floriculture industry, plan to attend the 31st Annual SAF Congressional Action Days, March 14-15, in Washington, D.C.; www.safnow.org/content/category/10/48/99.